In situations where a camera is physically separated from the user it is useful to provide a means to change its viewing direction and magnification. A camera that provides this is commonly referred to as a pan, tilt, and zoom camera, often abbreviated to PTZ. Control of a PTZ camera comes from a base station.
Current PTZ cameras rely on a mechanical apparatus to control the movement of the camera and its lens. This apparatus is heavy, expensive, prone to failure, and slow to respond.
The design of a mechanical PTZ camera can be found in U.S. Pat. No. 4,728,839 issued to J. B. Coughlan, et al, on Mar. 1, 1988. FIG. 1 shows the typical arrangement of a mechanical PTZ system. Video camera 15 may be a mechanical PTZ camera with zoom lens 1 connected to image sensor 2.
Image sensor 2 receives light through zoom lens 1 and sends a signal to image capture circuit 3, which captures an image or stream of images, for example, a real-time video feed, representing the light impinging on image sensor 2. Output circuit 5 transmits the captured image. Motors 4, including those for pan, tilt and zoom operations, may be integral or separate from video camera 15. Motors 4 are operated by signals from control circuit 6.
Base station 20 has receiving circuit 8 that receives the captured image from output circuit 5. The captured image is transmitted to both display circuit 9 and record circuit circuit 10. Display circuit 9 provides a view of the captured image, while record circuit 10 records the captured image(s). Control circuit 7 may receive input from a user directing video camera 15 to pan, tilt, or zoom. Control circuit 7 provides the appropriate inputs to control circuit 6.
It is common practice for surveillance cameras to signal an alarm on the basis of movement within the field of view. This commonly performed by comparison of the current video frame against a previous frame; if a region of the frame has changed sufficiently it is considered to be a moving object. Mechanical PTZ cameras suffer from the disadvantage that when zoomed in on a particular area they are unable to view other areas and so may miss important events.
Accordingly, what is needed is a system and method for zooming in on one particular area without loosing the ability to maintain security or a view of other areas.